1. Field of the Invention
This invention relates to a method and means for sealing valves or dampers of the type wherein a closure member is completely removed from the fluid stream. Valves or dampers of this type are often used to control the flow of high temperature gases in flue ducts.
2. Description of the Prior Art
U.S. Pat. No. 3,504,833 to Beck and U.S. Pat. No. 3,504,833 to Lowe et al. are both concerned with sliding gate valves and particularly with means for sealing the aperture through which a closure member is removed from the fluid stream when the valve is fully open. Both rely on the use of strips of spring steel bent into loops for closing the aperture and for accommodating the movement of the closure member through the aperture. The loops are disposed either about the aperture or on the end of the closure member.
Co-pending application Ser. No. 639,871 filed Dec. 10, 1975 in the name of the present inventor and Peter J. Connor discloses an aperture seal including a plurality of strips which overlap each other to seal the aperture when the closure member is removed entirely from the fluid stream and which resiliently engage the closure member when it is moved toward the closed position. The engagement of the strips with the closure member causes the strips to bend into a concave configuration with respect to the interior of the fluid passageway. A series of back-up plates are provided on the side of the strips which faces the exterior of the passageway to prevent the strips from buckling as the closure member is withdrawn from the passageway toward the open position. That is, the concave bending condition of the sealing strips caused by movement of the closure member toward the closed position is maintained by the backup plate when the closure member is moved in the opposite direction, i.e., toward the open position.
The aforementioned prior art devices utilizing resilient loops of spring steel have drawbacks in that the loops, while being readily deformable in cross section, are relatively inflexible along their length. In other words, the loops tend to have a uniform deformation along their entire length which prevents them from accommodating irregularities in the surfaces to be sealed.
Considerable irregularities on surfaces to be sealed are encountered in flue gas applications. In particular, flue gases contain particulate matter, acids, and, at certain stages of operation, condensed moisture. This all leads to corrosion and heavy deposits of adhesive dirt on materials exposed to the flue gases. The result is that the surfaces of the closure member of a flue duct damper become rough and highly irregular after a relatively short period in service. The loop type seal cannot effectively accommodate these irregularities. This problem, of course remains whether the loop type seal is disposed about the aperture through which the closure member moves or is disposed on the closure member itself. In the latter instance, the surface of the seals themselves will be subject to dirt deposits and corrosion.
The sealing strips disclosed in the aforementioned co-pending application may, unlike the loop seals, exhibit lengthwise flexibility, but they do not solve the problem of corrosion and dirt deposits on the closure member. As indicated, the strips are bent into a concave condition with respect to the interior of the passageway by the closure member as it moves toward the closed position. This concave bending configuration is maintained by retainer plates as the closure member is withdrawn, that is, as the closure member moves oppositely to the direction of bend and toward the open position. This will cause the irregularities on the surfaces of the closure member to catch the leading edges of the thin metal sealing strips causing tearing of the strips and other damage.